1. Field of the Invention
This invention relates in general to laser bump texturing of surface portions of magnetic recording disks, and more particularly to in-situ texture bump height measurement for improved texturing process control.
2. Description of the Prior Art
Contact start/stop (CSS) disk drives operate with a slider in contact with the disk surface during start and stop operations when there is insufficient disk rotational speed to maintain the air bearing. However, after a slider has been in stationary contact with the disk for a period of time, the slider tends to resist translational movement or xe2x80x9cstickxe2x80x9d to the disk surface, a problem known as xe2x80x9cstictionxe2x80x9d. To minimize the effect of stiction, CSS disk drives typically use a dedicated textured xe2x80x9clanding zonexe2x80x9d where the slider is parked when the drive is not operating. Typically, the disk substrate is textured before deposition of the magnetic layer and other layers that make up the magnetic recording disk. These layers replicate the texture of the underlying substrate and thus reduce the stiction where the slider is resting on the disk.
One technique for texturing the disk substrate is by pulsed laser radiation. U.S. Pat. No. 5,108,781, assigned to Magnetic Peripherals, Inc., describes a process for laser texturing by forming pits or craters in the substrate. U.S. Pat. Nos. 5,830,514, 5,550,696, 5,586,040, 5,822,211 and 5,658,475 describe devices and methods for laser texturing disk substrates. The problem discovered with current laser texturing devices and methods is that the average height of the laser-induced bumps can vary significantly from substrate to substrate, even when the substrates are presumably of the same material composition and the texturing laser energy is identical. Since the minimization of stiction is critically dependent on the average height of the bumps, it is necessary to develop a process that allows a texturing pattern with a known average bump height to be formed on all disks that are manufactured, thus assuring reliable operation of the disk drives into which the disks are incorporated. Additionally, the present invention facilitates the in-situ real time measurement of texture bump height, thus providing increased throughput as well as improved quality control in the disk texturing manufacturing process.
The invention is a method and apparatus for controlling the laser texturing of a magnetic disk using a textured laser system to create texturing bumps, and an analyzing laser system to determine texture bump height and to provide feedback to the texturing laser system. The analyzing laser system includes a scanning linear photodetector array that receives light diffracted from the textured disk surface to provide a digitized output that represents the angular distribution of diffracted light intensities. For crater shaped texture bumps the intensity of a first diffraction peak (Int1) and its array position (P1) are determined and utilized to calculate the average bump height h according to the equation:
h=A/P1+B(Int1)+C
where A, B and C are constants. This equation represents a functional relationship between laser energy and bump height over a range of laser energies that produce the crater shaped bumps. The values of A, B and C are determined for a batch of disks by taking a representative sample of disks and texturing them with differing laser energies within the energy level range. The average bump height h of each of the sample disks is determined using an ex-situ device, and also Int1 and P1 for each disk are determined in-situ using the analyzing laser system. The ex-situ and in-situ results for the sample disks are mathematically compared and the value of the constants A, B and C for the batch of disks is mathematically derived. The bump height of a first textured disk can thereafter be determined in-situ using the analyzing laser system and the equation with the known values of A, B and C. The energy of the texturing laser can then be adjusted, if necessary, to alter the bump height of a second, subsequent disk, where the in-situ determined bump height of the first disk is unacceptable. The present invention therefore provides real-time feedback in the disk texturing process, such that the bump height of each disk is determined, and feedback for the texturing of subsequent disks is obtained. Manufacturing efficiency and throughput are increased utilizing the present invention.
It is an advantage of the present invention that the average bump height of crater shaped texture bumps can be determined in-situ.
It is another advantage of the present invention that texture bump height is correlatable with texturing laser energy, such that the average bump height determination for a first disk can be utilized to provide feedback for creating texture bumps on a second, subsequent disk.
It is a further advantage of the present invention that the average texture bump height on each manufactured disk can be easily and rapidly determined.
It is yet another advantage of the present invention that real-time feedback of texture bump height is provided during the manufacturing process.
It is yet a further advantage of the present invention that manufacturing efficiency and throughput is increased during the disk texturing portion of the manufacturing process.
These and other advantages of the present invention will become well understood by those skilled in the art upon reading the following detailed description, which makes reference to the several figures of the drawings.